1. Field of the Invention
This invention relates generally to a method of providing a frequency selective surface on a coated substrate and, in one embodiment, to a method of laser marking, melting, ablating, or deleting a frequency selective surface into a solar control coating deposited on an automotive windshield blank.
2. Technical Considerations
In automotive transparencies, such as windshields and back lights, antennas for the reception and/or transmission of radio frequency (RF) waves (such as FM, AM, UHF, VHF, cell phones, etc.) are carried on or incorporated into the transparency. These antennas can be formed by electrically conductive, transparent films deposited onto the transparency or by metal wires or strips attached to the transparency.
In order to reduce heat build-up in the interior of the vehicle, the transparency can also be coated with a solar control film that absorbs or reflects solar energy. Such solar control films are usually transparent, electrically conductive films. Typically, the solar control film and the antenna are incorporated into a transparency such that the solar control film is either on the same surface as the antenna or is positioned outboard of the antenna.
A drawback of the solar control films is that they also reflect radio waves, which can impair or degrade the reception of the underlying antenna. Additionally, it is not uncommon for portions of the antenna and the conductive solar control film to form a galvanic connection through the transparency (commonly referred to as xe2x80x9ccouplingxe2x80x9d), which detunes the antenna and degrades its function.
In order to address the problems of RF energy reflection and coupling, the portion of the solar control film covering (i.e., outboard of) the antenna could be removed to facilitate the transmission of RF energy through that portion of the transparency to the antenna. However, removal of the solar control film would increase solar energy transmission into the interior of the vehicle, which can increase the vehicle temperature.
Another solution has been to cut slits in the solar control film to form what is commonly referred to as a frequency selective surface. By xe2x80x9cfrequency selective surfacexe2x80x9d is meant a coated surface which is relatively high in solar energy reflection and/or absorption but which also permits the passage of RF energy through the spaced narrow openings in the coated surface. For example, U.S. Pat. No. 5,364,685 discloses a panel in which a layer that is relatively high in radio wave reflectance is divided into a grid pattern having discontinuous square segments separated by a series of vertical and horizontal slits cut into the layer such that the width of each segment is not greater than {fraction (1/20)} of the wavelength of the radio wave to pass through the frequency selective surface. WO 96/31918 and U.S. Pat. No. 5,867,129 disclose other types of frequency selective surfaces.
In these known systems, the slits permit the transmission of RF energy through the solar control film while the remaining portions of the film provide solar control protection for the interior of the vehicle. While such slit patterns are acceptable, problems arise in the fabrication of slit patterns. For example, to provide a large area slit pattern using a single deletion device, such as a laser, the laser would have to be very accurately traversed across the length and width of the coating, necessitating the use of complex precision movement devices. Alternatively, multiple lasers could be used to form adjacent portions of the pattern. However, a problem arises in this multi-laser process in that the adjacent lasers must be carefully and accurately aligned such that a slit, such as a horizontal slit, formed by one laser can be continued uninterrupted by the adjacent laser to form a single continuous slit in the coating. Due to the intrinsic inaccuracy of the lasers or in the event the adjacent lasers become misaligned, the pattern formed by one laser can be offset from the pattern formed by another laser such that adjacent slits are not continuous, i.e., not aligned. This pattern offset degrades the effectiveness of the grid pattern by allowing relatively large areas of the conductive solar control coating to remain substantially intact, which can result in high RF energy reflectance and/or coupling with the adjacent area of the antenna, adversely affecting antenna performance.
Therefore, it would be advantageous to provide a method of making a frequency selective surface on a conductive coating that reduces or eliminates some of the problems described above.
The present invention provides a method of making a frequency selective surface in an electromagnetic energy attenuating coating having an electrical resistance, comprising: defining a first marking field and a first marking tolerance; defining a second marking field and a second marking tolerance; marking selected portions of the coating within the first marking field to define a first pattern; marking selected portions of the coating within the second marking field to define a second pattern such that the first and second patterns are spaced from one another by a distance at least equal to a combined tolerance of the marking devices; and marking a strip of the coating between the first pattern and the second pattern with at least one connector segment in a manner that substantially increases the resistance of the coating strip. In one nonlimiting embodiment, the coating strip marking comprises marking at least one connector segment within at least a portion of the coating strip interconnecting the first pattern and the second pattern. In another nonlimiting embodiment, the method further comprises depositing the coating on a substrate, combining the coated substrate with additional substrates to form a laminate, incorporating at least one antenna element into the laminate such that the at least one antenna element is spaced from the coating and adjacent to the first and second patterns.
The present invention also provides a method of making a frequency selective surface on a coated substrate, comprising: depositing a coating having a resistance on a substrate; forming a first pattern in the coating; forming a second pattern in the coating, wherein the first pattern and second pattern are separated by a strip of coating; and configuring the coating strip such that the resistance of the coating strip substantially increases.
The present invention further provides a coated substrate having a frequency selective surface, comprising: a substrate; an electromagnetic energy attenuating coating having a resistance deposited over at least a portion of the substrate; a first pattern marked in the coating; and a second pattern marked in the coating adjacent the first pattern, wherein the first pattern is separated from the second pattern by a strip of the coating configured to substantially increase the resistance of the coating strip. In one nonlimiting embodiment of the invention, the substrate further comprises at least one connector segment extending from at least in close proximity to the first pattern, through at least a portion of the coating strip to at least in close proximity to the second pattern. In another nonlimiting embodiment, the substrate is a laminated transparency comprising at least one glass ply and further comprising at least one antenna spaced from the coating and adjacent to the first pattern and second pattern.